Jump to content

Recommended Posts

@Dman Revolution Glad you are here! Looks like you can give @fourfa a run for his money! 

Unfortunately, this run won't count. First, because it is descending. Second, because it is over torqued. While this is not expressly forbidden, it violates the spirit of the competition. 

On another note: You say that your motors are clipped into fairings. From the pic, it looks like the props are exposed. Placing your props in a fairing is against the rules. 

Link to post
Share on other sites

Slight modification to my design. The big change is the placement of the props. I know the OP says "no extreme clipping/offset" so I don't know how you guys would classify offsetting the blades just enough to remove their rotational drag to remove the need for overclocking.

Also, to answer your question: The motors themselves are the only things in the fairings. The propellers are not.

yFAUnZE.jpg

8 minutes ago, Dman Revolution said:

Minor speed update:

ppQWdlU.jpg

Link to post
Share on other sites

I suspect at this point you might actually be running into prop blade speed curve issues. In general they don't like doing supersonic lift. Genuinely wonder if using conventional wings here might have some advantages.

 

Also I wonder if motor stacking would help? I remember my previous BG prop blade WR craft before they added the ducted fan blades using multiple motors to turn each prop. Of course, the optimal design back then was to avoid the prop reaching mach so thus low RPM high torque.

Might try making an entry later.

 

Edited by Pds314
Link to post
Share on other sites

Turning on Rigid Attach for every part on the spindle (all blades, even the nose cones) seems to enable 2x physics timewarp without glitching!  That alone makes these more usable in career...  Unfortunately it also seems to knock a dozen m/s off top speed

Addendum: the trailing-edge motors are the biggest single source of drag in my craft.  Enclosing them with a tightly-fitting fairing, closing on the motor spindle, does shield them from drag while leaving the moving part of the spindle and the blades outside the fairing.  Very tweaky but this is how I would set it up to use in career personally.

LBbO8dA.jpg

This got me to 364m/s.  I propose we allow motor fairings but be specific about what's OK and what's not

https://kerbalx.com/fourfa/Speed-Demon-3-364ms-stock-props

This version is really fun and easy to fly, I'm really happy with where this thread has gotten

Edited by fourfa
Link to post
Share on other sites

I'll just keep updating here. I'm having a lot of fun with these and hope to share the learnings...

So far I'm finding pretty consistently that max speed happens between 1200m and ~2000m.  I'm guessing it's the best balance between decreased fuselage drag and still-near-peak blade thrust.  Another effect has to do with number of blades per motor.  Here I was playing with number of RS-25 (the largest ducted-fan part) blades per EM-64S motor: 10, 12, 14, 16, 20.  At 10 and 12 I was nearly always pegged out at the 460 max rpm limit and getting lower speeds - so clearly the motor has surplus torque to spin more blades there.  20 would drop way down to 220rpm at max speed and lower speed - clearly too many blades.  14 was slightly better than 16 by 1-2m/s overall.  So I settled on 14 RS-25 per EM-64S and got an easy +35m/s here:

rUmmQZn.jpg

Going to repeat this with RS-12 on the EM-64s but I'm pretty sure 64 each is pretty close (56 and 72 are both slower than 64). This is a lot of part count, but it's a lot lower profile for small planes.  RS-25s on EM-64s look good on larger planes.  The ducted fan blades do seem to spank the regular props across the board FWIW. 

This Mk3 jumbo is super usable - one thing I hadn't appreciated is how short takeoffs and landings can be. The props control the speed very precisely, and you can approach your LZ at almost mach 1, slam on 10G of brakes by dialing blade pitch down to +7, and drop right down to 50m/s.  Then practically VTOL back again.  It's great fun on rough terrain.

Next, to try a streamlined speedster with the RS-25x14 motor...

Edited by fourfa
Link to post
Share on other sites

I've acheive 351 m/s by brute-force but I can't figure out how to shield engine from drag. An electric engine in a fairing won't spin. Each rotor have 16 blade R-25 and 2 EM-64, so a total of 4 EM-64 powered by 7 fuel cell array. As you can see rpm isn't at maxium so adding a third EM-64  will increase speed. My approach is that since rpm is limited, you can instead place the blade on a bigger part to increase their relative airspeed.

u0cr6EX.png

Edited by Mathrilord
Link to post
Share on other sites

Update: Third engine make it slower :/ 

Also getting many bugs

Engine or blade losing or gaining power every 5s

Strut + rotor = problem, lag in vab?????

symmetric fairing + rotor remove from symmetry + strut = more laggy and part deleting themself when placed.

sas going NAN don't want to stabilize

etc

Edited by Mathrilord
Link to post
Share on other sites
  • 2 weeks later...

I've got a question on the speed topic. I've built this, not for challenge but for fun.

xhEWFt1.jpg

At first I had 24 Blades on each pair of counterrotating rotor on each side. (So in total 96 blades). And this resulted in a slow speed of around 170 m/s. But after reducing to only 8 blades per rotor (In total 32 blades) the speed increased to 240m/s (235 m/s fully kerbaled). Why is it this way? I don't understand, how less blades make the plane go faster (as ksp does not simulate air turbulences near the blades)

I thought: moar propeller blades = moaaaar power!... but apparently, it's not...

And secondly: How can I get this plane go faster, apart from go-faster-lighting-stripes from 1.11 ;-) . Rotation and bladepitch are already controlled and fully maxed out in their influence. Is it only a matter of drag /mass reducing, or is there any magic i've overlooked. (SAS is needed, as it must compensate for some nasty torque on the x- and z-axis.)

 

As I said, it's not a challenge plane, it's a retro-looking kerbal transporter. But going faster is an idea that's tickeling me. 

 

Edited by Rakete
Link to post
Share on other sites
On 12/13/2020 at 4:41 AM, Dman Revolution said:

Slight modification to my design. The big change is the placement of the props. I know the OP says "no extreme clipping/offset" so I don't know how you guys would classify offsetting the blades just enough to remove their rotational drag to remove the need for overclocking.

Also, to answer your question: The motors themselves are the only things in the fairings. The propellers are not.

yFAUnZE.jpg

Minor speed update:

ppQWdlU.jpg

Could you share your craft file on KerbalX?

I'd like to take it for a ride and study your drag avoidance technique :wink:

My goal is ultimately to build an Eve SSTO with electric props but in order to make orbit I really need to eliminate drag...

I am currently at 363.6m/s with my test design - with some more blades I think I can push this to over 365 but i am not sure about 370+ so I need to eliminate more drag ;)

The R-12 blades show 4.5 kN of drag for my craft and clipping them in further on decreases thrust, not drag...

FcccpLj.png

 

This is single fuselage (obviously), dual motor and 52 blades per motor. Both engines are hidden in a fairing.

Edited by Fulgora
Link to post
Share on other sites

Well, I tried to use my own in-development mod to try to win this but the fact is that you all are simply much better aircraft designers than I.

I humbly release my creation in the hopes that it can help you beat the speed records and that I can be a part of it in that way.

@fourfaGood luck, mate.

Edited by Booots
Link to post
Share on other sites
  • 2 weeks later...

i came across this post searching for something else and it seemed right up my ally. I often find myself messing with prop planes trying to eek out every last m/s but i was blown away by the stuff you guys are coming up with. anyway, heres my best attempt so far at 349.7m/s:

tTnNAsV.jpg

GhaE3St.jpg

 

 

I tool a look at @fourfa craft with the fairing housed motors but i couldnt figure out what was going on there. i couldnt replicate it myself, wouldnt let me build the fairing, and i tried deploying the fairings from his to see what difference it made in speed and the motors just fell out haha. though to be fair ksp said i was missing something when i tried to load the craft in so that could have something to do with it. anyway, i took the idea of putting lots of the mid size ducted fan blades on although i could only get 6 sets of 8 to fit. and i didnt do any messing with fairings. though i remember someone somewhere saying shock cone intakes have the least drag out of all the nose cones, both leading and trailing so i went with those. im not sure how to upload the craft file elsewhere, but ill put it on the workshop called "8x6x2 solar prop plane".

Link to post
Share on other sites

so i did some studying on aero and had a close look at what was making drag and how much. so i did a couple redesigns and found all you really need is a pair of elevons to make lift. i found the actual wings to make too much drag and by the time i got the angle of attack of the craft to close to zero, the wings werent making any lift anyway. i still have the same motors and prop layouts as the last plane. i switched from solar power to fuel cells so i could put them in a cargo bay and have it all nice and tidy and making no drag.

so by getting it up over 340 then carefully managing the elevon angle so that the angle of attack was as close to zero as possible and VERY slowly increasing the prop pitch, im talking a tenth at a time, i managed to eek out 361.3. and this is still without putting the motors in fairings. i also took some video of going from 330+ to landing to show it actually flies pretty nice. im amazed at how much lift the elevon 5s make. although i guess once you pitch it up the mk2 parts are making lift as well.

Qbsl82J.jpg

 

EDIT:

i tried fitting a fairing around the motor and i was able to build it but i dont think i did it right as the motor was still making the same amount of drag. although after yeeting the fairings and dropping the drag THEY made, i got a little faster. 363 even. first pic is with the fairings still on, you can see the motors still make drag. next pic is after deploying them.

3fKc3qE.jpg

3M3D4uG.jpg

interesting side note, i was able to push drop the throttle a bit and push the prop pitch to 65 (the max in my KAL, probably wouldve gone higher) and kept it over 300m/s with each motor consuming under 9u/s.

EDIT again:

ok, im done. i promise. 365.3. still no fairings. still 6 sets of 8 blades. i did a lot of messing with the large rotor and you can easily reduce its drag to almost nothing by just slapping a cone on the back of it, but i couldnt get it much over 335 no matter what blades configuration i tried. so i came back to this plane and did another run for the heck of it.

kPYHWF2.jpg

Edited by Icky
new info gained relevant to post.
Link to post
Share on other sites

Awesome!  It really feels like there’s a natural limit there at like Mach 1.03.  Interesting that you found highest speeds scraping the water, when my nacelles always seemed to pick up a few m/s up around 1km. 

I kinda want to try all the absurd combinations of helicopter blades, and dissimilar blades on the same shaft, and more aero shielding shenanigans.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...